We all remember the story of David and Goliath, a tale that has become a trite metaphor for battles between the weak and the powerful. Knowing who's the big guy is easy, but in the realm of corporate combat, it isn't always clear which group has virtue on its side.

Consider the case of IBM versus TurboHercules, a tiny open source company trying to make a living selling mainframe emulator software. TurboHercules and its supporters claim that IBM is using its considerable patent muscle to stifle competition and browbeat the little company and, by extension, the open source community. IBM sees TuboHercules as a knockoff artist seeking to cash in on billions of dollars of Big Blue R&D and characterizes it as a Microsoft proxy.

There's some truth, I think, in both sides of this complex argument. There's also a big dose of overheated rhetoric around the issue, none of it helpful. Is IBM really a "hypocritical enemy of open source" and are we about to lose the right to open Word and Excel documents with OpenOffice? Is fair to compare TurboHercules, the product of 11 years of work, to the maker of "cheap knock-offs of brand-name clothing or apparel"? And can a tiny company really deal a serious blow to IBM's mainframe business?

I'm never shy about expressing an opinion (that's an understatement), but in this case, I'd rather present the facts as I know them and let you readers decide who -- if anyone -- is right.

Has IBM broken with open source?Roger Bowler founded the Hercules open source project about 11 years ago, and more recently he started TurboHercules in an attempt to make money from his work. The French company's software is an emulator that allows IBM's mainframe z/OS operating system to run on commodity servers.

According to Bowler, all he wants to do is strike a licensing deal for his customers with IBM: "We simply want IBM to agree to allow legitimate paying customers of its z/OS mainframe operating system to deploy that software on the hardware platforms of their choice -- including, should they so choose, on low-cost servers using Intel or AMD microprocessors and Hercules."

IBM refused, and when Bowler asked the company to reconsider, it refused again, sending him a letter last month that has outraged people like well-known open source activist Florian Mueller. First the letter, which you can read for yourself [PDF]: In it, IBM tells Bowler that it won't reconsider its decision to refuse a licensing deal and goes on to cite 173 patents that the emulator software might be infringing.